note that among the issues in slapo-rwm there's the fact that it's
attaching a callback structure on the thread's private data instead of
malloc'ing (and freeing) it when required. As a consequence, this may
prevent slapo-rwm from being called more than once in an operation
execution sequence, because it could result in an endless loop or
unexpected execution sequences. In fact, when used with a regular
database, multiple calls shouldn't occur (one would need to explicitly
add more than one instance of slapo-rwm on the same database, which
makes little sense). However, gluing more than one database which
independently needs slapo-rwm is one such case of multiple calls in one
thread execution.